M line

M line may refer to:

• M-line (mittel line or middle line), a structure in a muscle sarcomere
• M Ocean View, a light rail and former streetcar line in San Francisco, California
• M-Line Trolley, a streetcar line in Dallas, Texas
• M (Los Angeles Railway), a former streetcar service
• M (SEPTA Metro), a light metro in Montgomery County, Pennsylvania.
• Geometric mean

See also

• M Train (disambiguation), several train services
• M1 (disambiguation)#Railways
• Line M (disambiguation)